Trying to understand this pressure reading

[mbt]

Vw 2008 Rabbit/Golf

Ambient temperature 80F

Variable displacement Pxe-16

Charged with 18.5 oz R134a which is spec.

Static pressure at 80F was approx. 80 psi lo/hi

The reading at idle and 80F 35psi Lo & Hi

The reading at 2krpm low side 42psi to 20psi & High side some 25psi-50psi

[Tim]

Possible a bad control valve in the compressor.

[mbt]

Ok so a possible control valve issue, and not a blockage or restriction or issue with Txv?

[JohnHere]

The specifications that I have for your Rabbit are as follows: 23 ounces net weight of R-134a, and 4.5 fluid ounces of PAG-46. Specs for the same year Golf are a bit different.

[mbt]

Thanks, the label on the core support shows 525 +/- 25 g so 18.5 +/- 0.9 oz and confirmed with the factory repair manual with the same information.

[event3horizon]

Ok so a possible control valve issue, and not a blockage or restriction or issue with Txv?

See this is what's so difficult with a/c troubleshooting. I have, to date, not be able to find in depth information on how not to throw parts at a poorly performing system. In this case, how would you know it's the control valve or a faulty compressor just not producing enough pressure on the high side? I think a shop or dealer would just replace your compressor which comes with a valve and will not bother to just change the valve. However, changing the valve is a gamble as you've just spent $50+ dollars for it and more $ for a recovery/recharge only to find that it was a faulty compressor, for example. On top of all that, how would you rule out a TXV or not in this case? Wouldn't a faulty txv not affect the high pressure side to be so low? I'd think it will only affect the low side with higher than normal pressures if I'm not mistaken. So maybe you can rule out the TXV, but it seems to me as the car is a 2008 and how many miles? Perhaps it's time for a new compressor.